1. Field of the Invention
Embodiments of the present invention generally relate to a dynamic load lock chamber that is adapted to transfer one or more substrates from a first region that is at first pressure to a second region that is at a second pressure.
2. Description of the Related Art
Photovoltaic (PV) or solar cells are devices which convert sunlight into direct current (DC) electrical power. A typical PV cell includes a p-type silicon substrate with a thin layer of an n-type silicon material disposed on top of the p-type substrate. When exposed to sunlight (consisting of energy from photons), the p-n junction of the PV cell generates pairs of free electrons and holes. An electric field formed across a depletion region of the p-n junction separates the free electrons and holes, creating a voltage. A circuit from n-side to p-side allows the flow of electrons when the PV cell is connected to an electrical load. Electrical power is the product of the voltage times the current generated as the electrons and holes move through the external electrical load and eventually recombine. Each solar cell generates a specific amount of electrical power. A plurality of solar cells is tiled into modules sized to deliver the desired amount of system power.
The PV market has experienced growth with annual growth rates exceeding above 30% for the last ten years. Some articles have suggested that solar cell power production worldwide may exceed 10 GWp in the near future. It has been estimated that more than 90% of all photovoltaic modules are silicon wafer based. The high market growth rate in combination with the need to substantially reduce solar electricity costs has resulted in a number of serious challenges for silicon wafer production development for photovoltaics.
In order to meet these challenges, the following solar cell processing requirements generally need to be met: 1) the cost of ownership (CoO) for substrate fabrication equipment needs to be improved (e.g., high system throughput, high machine up-time, inexpensive machines, inexpensive consumable costs), 2) the area processed per process cycle needs to be increased (e.g., reduce processing per Wp) and 3) the quality of the formed layers and film stack formation processes needs to be well controlled and sufficient to produce highly efficient solar cells. Therefore, there is a need to cost effectively form and manufacture silicon sheets for solar cell applications.
Further, as the demand for solar cell devices continues to grow, there is a trend to reduce cost by increasing the substrate throughput and improving the quality of the deposition processes performed on the substrate. One challenge in this regard involves introduction of these fragile substrates from an atmospheric pressure environment into a low pressure processing environment. Traditionally, this involves moving a batch of substrates through a first slit valve opening, from an environment at atmospheric pressure into a load lock chamber, which is coupled to, but sealed from a low pressure processing environment using a second slit valve. The load lock chamber is then sealed from the atmospheric pressure environment using the first slit valve. The pressure is then slowly reduced within the chamber to at or near that in the processing chamber to prevent the movement of the low mass and fragile solar cell substrates. The solar cell substrates are then moved into the processing chamber through the second slit valve opening in the load lock chamber. The second slit valve is then closed and the load lock chamber is vented so that it can then receive the next batch of substrates.
However, this traditional load lock transfer process is time intensive and limits the processing capabilities of the entire production line, and thus, increasing the cost for producing the solar cell devices. To reduce this cost while also reducing surface contamination, there is a need for a design of a novel load lock chamber and process that enables high throughput, improved device yield, reduced number of substrate handling steps, and a compact system footprint.